1. Field of the Invention
The present invention relates to a water base ink for ink-jet recording to be used for an ink-jet recording method in which the water base ink for ink-jet recording is allowed to fly as minute liquid droplets from a recording head having a large number of pore nozzles to form a recorded image, and an ink-jet recording apparatus which accommodates the same.
2. Related Art
In the ink-jet recording system, ink droplets are formed by using an ink-jetting method including, for example, the electrostatic attraction method, the method in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element, and the method in which bubbles are generated by heating the ink to utilize the pressure generated thereby, and all or a part of the ink droplets are adhered to an objective recording material such as paper to perform the recording.
In relation to the ink for ink-jet recording to be used for the ink-jet recording system as described above, products of water base inks for ink-jet recording, which use water as the main solvent, have been hitherto vigorously developed. In particular, a water base ink for ink-jet recording, which uses a water-soluble dye as the coloring agent, has been used, because it is possible to obtain a high density recorded image with vivid color tone, no clog-up occurs in the ink flow passage or at the tip of the recording head of the ink-jet printer, and no discharge defect is caused because the water-soluble dye is completely dissolved in the ink solvent.
Recently, complex information composed of text letters and graphs or the like are printed in many situations in the office. In relation to the office use as described above, the recorded image is required to have the following characteristics which are regarded to be especially important. That is, the printing density is high. Letters and ruled lines are, for example, sharp and scarcely blurred. The water resistance is excellent.
In the case of the conventional water base ink for ink-jet recording which uses the water-soluble dye as the coloring agent, the water-soluble dye as the coloring agent is dissolved in the ink solvent. Therefore, the printing quality in relation to the blur or the like is approximately determined by the property of the ink solvent. It is difficult to obtain a printing quality in which the image is sharp and scarcely blurred. Further, the water resistance of the recorded image cannot be satisfactory, because the coloring agent is water-soluble.
On the other hand, a water base ink for ink-jet recording, which uses a pigment as the coloring agent, has been recently developed. Products are being vigorously developed, which utilize the characteristics of the pigment that is excellent, for example, in water resistance and light resistance. Further, a water base ink for ink-jet recording is also researched, which uses fine coloring resin particles colored with an oil-soluble dye or the like as an unique coloring agent which possesses both of the vivid color tone of the dye and the water resistance of the pigment.
In the water base inks for ink-jet recording based on the use of the particulate coloring agent such as the fine coloring resin particles and the pigment as the coloring agent, the coloring agent is not dissolved in the solvent, but the coloring agent is dispersed. Therefore, the printing quality is hardly affected by the blur of the ink solvent to advantageously obtain the printing quality in which the image is sharp and scarcely blurred, and the water resistance of the recorded image is also satisfactory, as compared with the case in which water-soluble dye is used as the coloring agent.
However, for example, the water base ink for ink-jet recording, which uses the particulate coloring agent such as a self-dispersing type coloring agent, involves such a problem that the particulate coloring agent is secured to the nozzle surface of the recording head. A problem has arisen such that it is extremely difficult to stably jet the ink from the recording head as compared with the case in which the water-soluble dye is used as the coloring agent.